The present invention relates generally to electrical power distribution and, more particularly, to the regulation of voltage in a distribution circuit to compensate for fluctuation in the load placed on the circuit.
It is widely recognized within the electrical utility industry that, under ideal conditions, electrical power should be delivered from distribution substations to distribution circuits at maximum voltage levels when current levels are highest during periods of peak load and, conversely, at minimum voltage levels when current levels are lowest during periods of relatively light load. As is well known, the amount of voltage originating in a distribution circuit from its distribution substation determines the current or load capacity of the circuit and the distance along the circuit to which customers can be supplied with adequate voltage. As will be apparent, if the level of voltage delivered to a customer is too low, the voltage will be insufficient to properly operate the customer's electrical devices and appliances and, further, can potentially damage the devices and appliances. On the other hand, excessive voltage for the prevailing current in the distribution circuit poses a danger of damaging transformers in the circuit as well as potential damage to customers' electrical devices and appliances, while also representing a substantial waste of electrical energy.
Conventional approaches to the ongoing problem of load variations in electrical distribution circuits are largely inadequate. Under one approach, when the sustained current levels under peak load conditions have increased over time in a distribution circuit to the point that the circuit cannot adequately service customers, the electrical transmission lines in the circuit may be replaced with transmission lines offering lesser electrical resistance so that voltage is maintained at an adequate level at a greater distance along the distribution circuit from the substation. However, this technique, commonly referred to as reconductoring, is very expensive, costing as much as $20,000 to $30,000 per mile of power distribution line. Further, reconductoring does not provide the distribution circuit with any ability to adjust or compensate for voltage fluctuations in the distribution circuit resulting from changing loads placed on the circuit.
To address this latter problem, a distribution circuit transformer may be equipped with a so-called tap change under load (TCUL) voltage regulator which is operative to maintain the voltage output from the transformer within a maximum-minimum band width or range, typically three volts. Thus, if the prevailing voltage leaving the transformer exceeds the predetermined maximum voltage, the TCUL regulator lowers the voltage output to the upper limit of the acceptable range. Conversely, if the voltage output from the transformer falls below the predetermined minimum voltage, the regulator increases the voltage output of the transformer to the lower limit of the range. As will thus be understood, when the load on the distribution circuit is sufficiently high to reduce the voltage output from the transformer below the lower limit of the established band width, the regulator will merely insure a minimum voltage output from the transformer whereas optimally the voltage output should be maximized under such conditions. Conversely, under conditions of sufficiently light loading on the distribution circuit to cause the voltage output from the transformer to exceed the predetermined maximum limit of the band width, the regulator will merely insure that the voltage output of the regulator is limited to a maximum voltage level, whereas a minimum voltage would be optimal under such conditions.
Voltage regulators of the TCUL type may also be provided with a voltage compensation arrangement by which the maximum-minimum voltage band width is automatically adjusted upwardly and downwardly in relation to fluctuations in the current in the distribution circuit over the course of time. Such compensation arrangements suffer several disadvantages, however, which have prevented the widespread acceptance and practical implementation thereof. In order to program a compensation arrangement to properly control adjustment of the voltage band width of the associated voltage regulator, various control settings must be made both on the basis of predictions of future expected fluctuations in the loading of the distribution circuit and on the basis of regular monitoring of the voltage regulator. Quite obviously, the prediction of future current fluctuations in a distribution circuit, particularly the timing and current levels under peak loading conditions, is virtually impossible beyond very general predictions and estimates which are of insufficient accuracy to provide a basis for establishing reliable settings. On the other hand, the ongoing monitoring, calculations and periodic re-setting of a compensation arrangement is so highly labor intensive as to largely offset the purported benefits of voltage compensation. Importantly, conventional voltage compensation arrangements have no means of limiting the upward adjustment of the voltage band width of the voltage regulator. Accordingly, without frequent monitoring and re-setting of conventional compensation arrangements, the voltage band width will gradually be adjusted upwardly as the peak current levels experienced in the distribution circuit naturally increase over time, to the point that the output voltage from the associated transformer will be undesirably high.